This application claims priority to an application entitled xe2x80x9cAPPARATUS FOR MEASURING ABSOLUTE ANGLE AND METHOD THEREOFxe2x80x9d applied with the Korean Industrial Property Office on Dec. 30, 2000 and assigned Serial No. 2000-87187, the contents of which is hereby incorporated by reference.
1. Field of the Invention
The invention relates to an apparatus for measuring an absolute rotation angle and a method thereof. In particular, the measuring apparatus is available for a measurement and servo system in which high precision is required in rotation drive and absolute rotation angle measurement.
2. Description of the Related Art
In a number of measuring and servo systems for performing rotation drive, higher precision has been required in rotation drive and absolute rotation angle measurement. Also, in the most cases of this rotation drive system, it is being required to carry out absolute rotation angle measurement in real time. At the present, a rotation angle sensor, which measures a relative or absolute rotation angle according to a measured rotation angle, includes an encoder, a resolver, a synchro and the like. Lately, a multi-speed resolver is frequently used for improving precision. However, in measuring the rotation angle by using the multi-speed resolver and a normal RDC (Resolver to Digital Converter), an absolute rotation angle can be measured within a limited angle, whereas only the relative rotation angle can be obtained beyond the range of the limited angle as a problem.
FIG. 1 shows a structure of a general resolver, and FIG. 2 shows input-output signals of a general resolver and digital outputs from an RDC.
Referring to FIG. 1, the resolver has one rotor 12 and two stators 14 and 16. When the rotor 12 is energized with an AC square wave as shown in FIG. 2, sine and cosine signals are obtained from the stators 14 and 16. In the one-speed resolver as shown in FIG. 1, the absolute rotation angle can be measured easily by using the RDC which digitalizes the outputs of the resolver. On the other hand, the multi-speed resolver, for example a two-speed resolver has relatively high precision. However, the multi-speed resolver has output waveforms like two-speed outputs E1 and E2 as shown in FIG. 2. Accordingly, the relative rotation angle cannot be obtained beyond the limited angle while the value of the absolute rotation angle is provided within the limited angle.
It is therefore an object of the present invention to provide an apparatus and method available for a digital measurement and servo system for measuring the value of an absolute rotation angle very precisely.
According to an embodiment of the invention to obtain the object, it is provided an apparatus for measuring an absolute rotation angle, comprising: a rotation mechanism having a driver rotating unit connected to a resolver, a driver fixing unit coupled to the driver rotating unit and a sensor for detecting a rotating state of the driver rotating unit; an actuator unit for driving the rotation mechanism in response to a rotation control; a resolver interface for converting a rotation detection signal from the resolver to a digital resolve data; and a controller for providing the rotation control signal to the actuator unit, receives the digital resolver data and the rotation detection signal to set the initial rotation reference position of the rotation mechanism, and compensates a rotation angle when the digital resolver data changes abruptly in respect to the initial rotation reference position to calculate an absolute rotation angle.